Printing materials can be processed in presses in both sheet form and web form. Sheet-fed rotary presses or web-fed rotary presses are used in these instances. Sheet-fed rotary presses process printing material that is cut into sheets. The sheets are inserted into a feeder in stacks and from there are transported separately sheet by sheet through the press. With this arrangement, individual partial images can be applied in various printing units during sheet transport. The sheet-fed rotary press also can be configured to carry out so-called sheet turning in such a way that, after the sheet turning, the side of the printing material opposite the previously printed sided can be printed. Furthermore, a series of additional operations can be carried out within a sheet-fed rotary press. For instance, a drying system can be provided between the printing units. A coating of a varnish or special ink also can be provided before or after the printing units. Further processing operations in the form of punching, embossing, creasing, perforating or cutting operations can be carried out before, between or after the printing units. The press can also be connected to a quality control system, which envisages removing sheets from the sheet run.
Web-fed rotary presses are known for conveying the printing material through the machine in web form. With such presses, the printing material is taken from a roll and drawn continuously through the press. As a rule, the printing material is simultaneously printed from both sides. The configuration of the printing units can be very different and depends on the type of printing process and the end product. With a web-fed rotary press, different printing processes are known. The printing process for web-fed rotary presses can be offset printing or planographic printing, it can be flexographic printing or letterpress printing or use can be made of a gravure printing process. With web-fed rotary presses, printing inks of extremely different qualities can be used, depending on which of the aforementioned printing processes are used. For example, in flexographic printing and gravure printing, solvent-containing inks are used. As a result of the comparatively simple design of the web-fed rotary press, a protection mechanism for ensuring that solvent cannot escape outside the machine can be incorporated into the press quite easily.
The disadvantage with sheet-fed rotary presses is that processing using letterpress printing or gravure printing in conjunction with solvent-containing inks is relatively difficult. The disadvantage with the web-fed rotary press is that the press format cannot be varied and the printing material format used in the press is virtually fixed.